Q:

How does water boil?

A:

According to Elmhurst College, the molecules in a liquid are packed closely together and make random movements, as the molecules slip past each other. As the liquid is heated, the kinetic energy increases, which causes the motion of the molecules to increase. Eventually, the motion becomes so intense that the forces of attraction between the molecules are disrupted, and the molecules break free of the liquid, becoming a gas.

Since the polarity of the molecules determines the forces of attraction between the molecules in their liquid state, different molecules have different boiling points. In water, molecules that are bonded by hydrogen bonding present a special case of polar dipole forces exerting a very strong effect to maintain the liquid state. When compared to similar molecules in Group VI of the periodic table, water has an abnormally high boiling point of 100 degrees Celsius. If water behaved as a normal polar molecule, it would boil at about -100 degrees Celsius.

According to Wikipedia, adding a water-soluble substance, such as salt or sugar, increases the boiling point of water. Even though adding salt, in this way at a palatable level, will barely make a noticeable difference, it is possible to notice the difference in boiling point by adding salt.


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